Since a polyethylene resin does not have a polar group, said resin has problems that (1) said resin is unsatisfactory in its adhesive property with an inorganic material or a metal, coating property and printing property, and (2) a polymer alloy obtained by blending said resin with a polar group-containing polymer (particularly, what is called, an engineering plastic such as a polyester resin, a polyamide resin, a polyphenylene sulfide resin and a polyphenylene oxide resin) is unsatisfactory in its mechanical strength such as impact resistance, and as a result, a molded article comprising the polymer alloy peels easily in its surface.
In order to solve these problems, there is generally known a method of graft-modifying the polyethylene resin, wherein the polyethylene resin, a polar group-containing compound and a radical-generating compound such as an organic peroxide are melt kneaded in a kneading extruder in order to graft the polar group-containing compound onto the polyethylene resin (JP 3-41105B and JP 3-76327B).